Summer is a time for hands-on discovery, curiosity-fueled learning, and of course—STEM adventures that make science come alive! Our latest Summer of STEM experiment gave students the chance to explore the relationship between pressure, density, and buoyancy using a simple but fascinating experiment: the Ketchup Bottle Cartesian Diver.
This classic STEM activity uses everyday materials to create a miniature diver inside a bottle that sinks and floats with just the squeeze of a hand.
What We Did
Each student received a clear plastic water bottle, a ketchup packet (our “diver”), and a tub of water for testing. With careful teamwork and trial-and-error, the children selected packets that floated just enough inside the bottle. Once the bottles were sealed, the real magic began!
With a firm squeeze, the ketchup packet sank. Release the squeeze, and it popped back up! While the children observed we discussed and predicted what would happen with each change in pressure.
What We Learned
This experiment helped children explore buoyancy, air pressure, and density in action. When the bottle is squeezed, pressure forces water pressure into the ketchup packet, compressing the air bubble inside and making it denser and heavier—and it sinks. Letting go decreases the pressure, allowing the air bubble to expand, and the diver floats to the top again.
It was a perfect introduction to the principles of fluid mechanics, all through playful exploration. As always, our students were encouraged to ask questions, test ideas, and draw their own conclusions.
STEM in Action
Throughout the activity, students were guided to think like scientists and engineers:
- Observe how different ketchup packets behave
- Predict how much pressure would make the diver sink or rise
- Test their hypotheses with multiple tries
- Reflect on how the system worked and why
Each step of the process encouraged critical thinking, teamwork, and hands-on engagement—core elements of DreamSpark’s approach to STEM learning.
Why We Love It
The Ketchup Bottle Cartesian Diver is more than just a fun trick—it’s a memorable way for kids to connect scientific theory to real-world applications. Plus, it shows how science can happen anywhere—even with a bottle, some water, and a ketchup packet from lunch!
We love giving our students opportunities to explore big ideas with simple materials. These early experiences build confidence, curiosity, and a lifelong love for learning.
Stay tuned for more Summer of STEM fun as we continue to dive into hands-on science every week. And if you want to try this activity at home, just grab a bottle, a ketchup packet, and a little curiosity—it’s time to make science float!
